The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods and structures to form voltage detection circuits that would detect the point at which a voltage reached a certain value. One application for such voltage detection circuits was as an under-voltage lock-out (UVLO) circuit for a switching power supply controllers. One example of such a switching power supply controller was the NCP345 that was available from ON semiconductor of Phoenix Ariz. The prior switching power supply controllers typically formed a switching drive signal that was used to switch a power transistor to produce a regulated voltage. In switching power supply controller applications it was important to prevent driving the power switch of the power supply controller if the input voltage was less than a minimum desired operating value. These prior UVLO circuits generally had a power dissipation when the input voltage was below the desired operating value that was approximately equal to the power dissipation when the input voltage was above the desired operating value.
Another type of voltage detection circuit was disclosed in U.S. Pat. No. 6,605,978 issued to Halamik et al on Aug. 12, 2003. This type of voltage detection circuit consumed less power than the prior UVLO circuits, however, this type of circuit generally had less accuracy.
Accordingly, it is desirable to have a voltage detection circuit that has low power dissipation, and that has accurate detection of at least the lower threshold value of the input voltage.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay between the reaction that is initiated by the initial action.